Procedural sprite 2D depth drawing

I have made script that generates separate parts of image, creates new sprites and packs them to atlas.

What I want is to add some depth effect to sprite.

After several attemts got interested if anyone already made something like that. So instead of inventing a wheel I desided to ask a question here.

What I want to achieve:

• taking custom sprite with alpha values
• creating depthlike overlay on that sprite
• creating new sprite from it

Added example of depth I want to get.